JP4464006B2 - Imaging apparatus and exposure method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus such as a digital camera and an exposure method thereof.
[0002]
[Prior art]
In a digital camera, means for controlling the exposure time of an imaging element (light receiving element) such as a photodiode (PD) is divided into the following two types. One is a mechanical shutter (mechanical shutter; hereinafter abbreviated as “mechanical shutter”) that physically blocks light irradiation from the object scene. The other is an element shutter that substitutes for a shutter by switching energization of the image sensor, that is, an electronic shutter.
[0003]
Of these two types of shutters, the mechanical shutter is mainly used in an interlace scan type digital camera. In the interlace scan method, the odd-numbered and even-numbered scan lines are alternately read out, so that the image sensor that constitutes the other scan line does not receive light while one scan line is being scanned. This is because it is necessary to completely block the light from the light.
[0004]
On the other hand, the electronic shutter discards the signal charge accumulated in the image sensor in the direction of the substrate using a vertical overflow drain (VOD). As a result, the image sensor can start exposure from the state where the signal charge becomes zero. Therefore, the electronic shutter is used for the progressive scan method. This is because in this method, since all pixels are read out at once, it is not necessary to shut off the light source unlike the interlace scan method.
[0005]
Although it is possible to perform the exposure time control only with the electronic shutter, as described above, when the exposure time control is performed using only the electronic shutter in the interlace method, the difference in reading for each scanning line becomes too large, It cannot stand practical use. Moreover, although it can be used for the progressive method, light from the object field is not completely blocked, so that smear may occur due to an intense light source during reading of signal charges.
[0006]
From this point of view, it is preferable to start exposure with an electronic shutter capable of high-speed switching, and to end exposure with a mechanical shutter that can completely shut off the light source. However, the mechanical shutter has a problem in slow shutter speed. This is because if the shutter is closed after a desired timing due to the mechanical delay of the mechanical shutter, the charge due to the excess light amount is accumulated in the image sensor and the signal charge overflows.
[0007]
Therefore, in order to overcome the slow shutter speed while taking advantage of the mechanical shutter, a method using an electronic shutter and a mechanical shutter in combination has been proposed. For example, in Japanese Patent No. 2649882 and Japanese Patent No. 2649883, the exposure start is performed by an electronic shutter, and the exposure end is performed by a mechanical shutter. The error due to the mechanical shutter delay is compensated by fine adjustment on the electronic shutter side.
[0008]
[Problems to be solved by the invention]
However, in the case of the above prior art, there is a time lag due to fine adjustment by the electronic shutter before the exposure is actually started even when the blanking period or the like is ended and the exposure mode is started. There is a drawback that an object to be missed is missed.
[0009]
Further, although one mode (exposure mode) is assigned for exposure, time is wasted due to the time lag, and the period of the exposure mode is unnecessarily extended. This causes performance degradation such as a reduction in the number of continuous shots. In order to solve this, a method of optimizing the imaging time by assigning a time of “camera shake limit time + mechanical shutter closing time” as the exposure mode can be adopted, but the exposure time is less than the camera shake limit time Is still a waste of time.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to provide an image pickup apparatus and an exposure method that eliminate such drawbacks of the prior art and that start exposure with little or no time lag from shifting to an exposure mode.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention includes a plurality of two-dimensionally arranged imaging elements that photoelectrically convert incident light from an object field into signal charges and store them, and at least a movie mode, an exposure mode, or a signal An imaging apparatus that operates according to an operation mode selected from among the readout modes has the following features.
[0012]
That is, this apparatus is a unit that is integrally connected to an image pickup device that calculates a desired exposure time based on the amount of incident light irradiated from the object scene, and a charge that can extract signal charges accumulated in this device. It is connected to the extraction means, the charge extraction means and the image sensor, and is usually in the movie mode, and it is possible to switch the operation mode in synchronization with the synchronization signal transmitted by itself, and when the operation mode is switched to the exposure mode. At the same time, the charge extraction means is instructed to extract the signal charge at least once over a predetermined period, and when the operation mode is switched to the signal readout mode, the signal charge accumulated in the image sensor is read out. A signal generation means for instructing the image sensor, and a device that is normally open and physically shuts off the image sensor from the object scene by being closed. An exposure adjustment means connected to a mechanical shutter means, an exposure adjustment means for opening and closing the means, a calculation means, a signal generation means and an exposure adjustment means, and receiving the exposure time calculated by the calculation means; When the operation mode switching instruction is transferred to the signal generation means and the operation mode is the exposure mode, the exposure adjustment means is set so that the mechanical shutter means closes simultaneously with the end of the exposure time that starts as the predetermined period elapses. Control means for controlling.
[0013]
According to the present invention, exposure is performed by an instruction to switch to an exposure mode transferred from the control means to the signal generation means, and signal charge is read by an instruction to switch to the signal readout mode transferred from the control means to the signal generation means. Is done.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of an imaging apparatus and an exposure method for the imaging apparatus according to the present invention will be described in detail with reference to the accompanying drawings. In addition, illustration and description are abbreviate | omitted about the part which is not directly related to this invention. Further, a reference symbol of a signal is represented by a reference number of a connection line in which the signal appears.
[0015]
FIG. 1 shows a case where the imaging apparatus of the present invention is applied to a digital camera 10. As shown in FIG. 1, the digital camera 10 includes an imaging system 10A, a signal processing system 10B, a drive signal generation unit 10C, a signal output system 10D, a mode designation unit 10E, and a system control unit 12.
[0016]
The imaging system 10A includes an imaging lens 102, an imaging unit 104, an AF (Auto Focus) adjustment unit 106 including a focus adjustment mechanism (not shown), an AE (Auto Exposure) adjustment unit 108, and an imaging unit 104. It includes a mechanical shutter mechanism (hereinafter abbreviated as “mechanical shutter”) 108d on the light side. The mechanical shutter is normally opened, and can be physically completely blocked from incident light from the object field irradiated on the image sensor of the image capturing unit 104 by being closed. The mechanical shutter is driven by a drive signal 108c described later, but has a feature that it takes a certain time to open and close. The imaging lens 102 is an optical system that condenses incident light from the object scene so as to focus on the light receiving surface of the imaging unit 104.
[0017]
Although not shown, the imaging unit 104 includes an imaging element (light receiving element) such as a photodiode (PD) that photoelectrically converts supplied incident light, and these are arranged in a grid pattern in the row direction and the column direction. A light receiving surface is formed in a two-dimensional array. The arrangement of the imaging elements may be a honeycomb-like arrangement in which the grid-like arrangement is shifted vertically and horizontally and the pixel column interval is 1 / √2 times. The image pickup unit 104 is provided with a color filter segment that separates incident light from the image pickup element on the incident light side, and is integrally formed as a color separation filter CF that forms a single plate corresponding to each of the image pickup elements. ing. With the arrangement of the color separation filter CF, incident light that has been color-separated so as to have the respective color attributes of the three primary colors RGB, for example, is incident on the image sensor. The imaging unit 104 outputs the imaging signal 10a to the signal processing system 10B.
[0018]
Further, the configuration of the imaging unit 104 will be described. A transfer gate (signal readout gate) that prevents leakage of signal charges is provided between the image pickup device constituting the image pickup unit 104 and a transfer device (not shown) that is disposed adjacent to the image pickup device, that is, a vertical transfer device. Is formed. The transfer gate opens and closes the gate in response to a field shift pulse included in the vertical synchronization signal supplied through the electrode, and transfers (field shift) the signal charge from the image sensor to the vertical transfer path. The vertical transfer path is configured by a charge coupled device (hereinafter, referred to as CCD), and sequentially transfers the read signal charges in the column direction, that is, the vertical direction in response to the vertical synchronization signal VD. By vertical transfer, the signal charge is line-shifted and supplied to a transfer element in the row direction, that is, a horizontal transfer path. The horizontal transfer path is also composed of a CCD, and responds to the supplied horizontal synchronization signal and outputs the signal charge to the signal processing system 10B as the signal 10a through the amplifier as described above.
[0019]
In addition to this, the imaging unit is provided with a vertical overflow drain (VOD) that is disposed on the substrate side with respect to the imaging element, although not shown. The VOD is an element that extracts signal charges accumulated by the image sensor in the direction of the substrate by a reverse bias voltage applied to the substrate. Thereby, an electronic shutter function for extracting signal charges at high speed is realized.
[0020]
As described above, the imaging unit has two types of means for removing charges from the imaging device. One is a transfer gate and the other is an electronic shutter. Exposure is newly started from the time when charges are extracted from the image pickup device by these means, which will be described later in the description of the operation of this embodiment.
[0021]
A signal for driving the imaging unit 104 is a drive signal 122a output from a drive signal generation unit 10C described later. This includes a line shift pulse and vertical / horizontal synchronization signals VD / HD in addition to an electronic shutter drive signal or transfer gate drive signal (field shift pulse) for extracting signal charges from the image sensor.
[0022]
The AF adjustment unit 106 arranges the imaging lens 102 at an optimal position according to information obtained by measuring the distance between the subject and the camera 10 using a focus adjustment mechanism (not shown specifically). This position adjustment is performed. At this time, the distance measurement information is calculated by the signal processing unit 114 in the subsequent stage, and the distance measurement information is processed by the system control unit 12 to determine the control amount. As a result, according to the supplied control signal 12a, the AF adjustment unit 106 drives the focus adjustment mechanism with the drive signal 106a, and moves the imaging lens 102 along the optical axis in the direction of arrow A.
[0023]
The AE adjustment unit 108 supplies the drive signal 108a to the aperture shutter mechanism 108b by the control signal 12a from the exposure calculation control function unit 12A in the system control unit 12 in which the photometric value of the object scene including the subject is calculated. Then, the aperture position is displaced to adjust the amount of incident light flux. Further, the AE adjustment unit 108 supplies a drive signal 108c to the mechanical shutter mechanism 108d to give an opening / closing timing, and opens / closes the mechanical shutter 108d accordingly. The light shielding timing of the mechanical shutter 108d is also given by the control signal 12a from the system control unit 12. The control signal 12a may be supplied separately for AE adjustment and AF adjustment.
[0024]
The signal processing system 10B includes a preprocessing unit 110, an A / D conversion unit 112, a signal processing unit 114, a buffer unit 116, and a compression / decompression processing unit 118. The signal processing system 10B is supplied with a control signal 12b from the system control unit 12 so as to control the above-described units in accordance with the mode, and timing signals 20a to 20e, respectively. The preprocessing unit 110 is connected to the output 10a of the imaging system 10A. For example, the signal charge 10a supplied is subjected to correlated double sampling (CDS) processing to reduce noise, and the signal is gamma corrected. The signal 10a is amplified and output to the A / D converter 112. These preprocessing are performed in synchronization with the timing signal 20a. The gamma correction is not limited to this position, and may be performed by the signal processing unit 114 at the subsequent stage.
[0025]
The A / D conversion unit 112 is connected to the output 10b of the preprocessing unit 110, and is supplied via the preprocessing unit 110 using the control signal 12b and the timing signal 20b from the system control unit 12. Are sampled and quantized into a digital signal (or image data) 10c. The timing signal 20b may be a clock signal when high-speed processing is performed. The converted digital signal 10c is supplied to the signal processing unit 114. In this embodiment, the system control unit 12 is caused to perform processing and control related to the control of the AF adjustment unit 106 and the AE adjustment unit 108. For this reason, the digital signal 10c is also supplied to the system controller 12 as shown in FIG.
[0026]
The signal processing unit 114 is connected to the output 10c of the A / D conversion unit 112, and performs commonly performed white balance adjustment (AWB), aperture correction, and the like. The signal processing unit 114 can be set to perform processing (AE) for calculating an automatic aperture value. In this embodiment, this AE process is performed by the exposure calculation control function unit 12A. The signal processing unit 114 performs these processes and further performs signal processing according to each of the three modes. In the present embodiment, for example, all pixels, two-line thinning, and frame reading are set as the signal reading mode according to the recording capacity and the image quality to be recorded by the key switch 130 described later. In the movie mode, the image of the imaging system 10A is simply displayed, and photometry including AF and AE is also performed. The photometry is set to two-line thinning-out reading because of high speed requirements. In this configuration, the mode is not limited to three types, and a larger 1/4 thinning may be used.
[0027]
As will be described later in this embodiment, this photometry and control is performed with the exposure calculation control function unit 12A provided in the system control unit 12, but the signal processing unit 114 performs optimal exposure of the object scene. Arithmetic processing may be performed. In this case, the signal processing unit 114 calculates the photometric value using the data of the predetermined area of the supplied image data 10c, and calculates the aperture value and the exposure time based on the calculated photometric value. The signal processing unit 114 supplies the value 10c obtained by the calculation to the system control unit 12. The system control unit 12 generates a control signal 12a corresponding to the supplied value and supplies it to the imaging system 10A.
[0028]
In addition, in the digital still camera 10, which mode is currently selected is controlled by the control signal 12b described above. Under the control of the system control unit 12, in the signal processing unit 114, in addition to the above-described signal processing, signal processing accompanying predetermined digital in the signal readout mode, for example, high-bandwidth of the luminance signal is performed.
[0029]
The signal processing unit 114 converts the imaging signal 10a from the imaging unit 104 into a recordable video signal by signal processing in the signal readout mode. Then, the signal processing unit 114 outputs the signal 10d in the mode in which display / recording is selected to the buffer unit 116.
[0030]
The gamma correction processing described above may be performed here or may be performed at a later stage. Since the series of signal processing is performed digitally, the signal processing unit 114 may be configured in a DSP (Digital Signal Processor).
[0031]
The buffer unit 116 is connected to the output 10d of the signal processing unit 114. The buffer unit 116 amplifies the supplied video signal 10d to a predetermined amplitude, and also has a function of adjusting time during recording. The buffer unit 116 outputs the image 10e to the signal output system 10D or the compression / decompression processing unit 118 under the control of a recording control unit (not shown) arranged in the system control unit 12.
[0032]
The compression / decompression processing unit 118 is connected to the output 10e of the buffer unit 116, and captures and records the image signal 10e by the control signal 12b from the system control unit 12. The supplied image signal 10e is subjected to compression processing based on, for example, JPEG (Joint Photographic coding Experts Group) standard. Further, when reading and reproducing the signal 10f recorded from the recording / reproducing unit 126, the original image signal is reproduced by performing signal processing such as inverse conversion of the compression processing described above, and is restored although not shown. The image signal is supplied to the display unit 124 and displayed.
[0033]
The signal output system 10D includes a display unit 124 and a recording / reproducing unit 126. The display unit 124 is connected to the output 10e of the buffer unit 116, and includes a VGA (Video Graphics Array) standard liquid crystal display monitor with digital RGB input, for example. The recording / reproducing unit 126 is a storage unit, and records a video signal 10f supplied to a semiconductor memory, a magnetic recording medium, an optical recording medium, or a magneto-optical recording medium used for a memory card or the like. The recording / reproducing unit 126 can also read the recorded video signal 10f and display it on the display unit 124. When the recording / reproducing unit 126 can detach the recording medium, only the recording medium may be removed and a video signal recorded by an external device may be reproduced and displayed or an image may be printed. These are controlled by a control signal 12c.
[0034]
The mode designation unit 10E is provided with a shutter release button 128 and a key switch 130, and is a device that determines the operation mode of the digital camera 10. The operation mode here refers to at least three modes of an exposure mode and a signal readout mode for photographing the obtained still image and taking them into the recording / reproducing unit 126 of the signal output system 10D, and a movie mode for simply displaying a moving image. means. The shutter release button 128 is a push button having a two-step push function in this embodiment. When the shutter release button is not pressed, the movie mode is set, which is the initial mode. In the first-stage half-pressed state, the instruction signal 28 for performing metering, which will be described later, is output to the system control unit 12 in the movie mode, and in the second-stage fully depressed state, the exposure mode switching signal 28 is controlled by the system. Output to part 12.
[0035]
The key switch 130 sets the CCD signal readout method according to the mode. For example, in the case of performing photometry, it is necessary to read out at high speed, and reading is performed by thinning out two lines. In addition, all pixel readout and frame readout can be selected. The selected information is sent to the system control unit 12 via the signal line 30.
[0036]
The system control unit 12 is a controller that is connected to the outputs 28 and 30 of the mode designating unit and controls the operation of the entire camera. The system control unit 12 includes a central processing unit (CPU). The system control unit 12 determines which mode is selected by an input signal (or designation signal) 28 from the shutter release button 128. However, the actual mode switching is performed by the timing signal generation unit 120 as described later. In addition, the system control unit 12 controls reading of the image signal of the camera based on the selection information 30 from the key switch 130. As described above, the system control unit 12 supplies the operation mode information 12b to the signal processing system described later based on the information supplied from the mode specifying unit 10E. Further, a reset signal for supplying the selected mode switching instruction 12d to the timing signal generation unit 120 of the drive signal generation unit 10C, which will be described later, and resetting the vertical synchronization signal VD generated by the timing signal generation unit 120. 12e can be output.
[0037]
As described above, the system control unit 12 is provided with the exposure calculation control function unit 12A and the recording control unit. The recording control unit controls operations of the buffer unit 116 and the recording / reproducing unit 126 of the signal output system 10D according to the control signal 12c from the system control unit 12.
[0038]
The exposure calculation control function unit 12A performs photometry in the movie mode. When the metering instruction signal 28 is input to the system control unit 12 when the shutter release button 128 is half-pressed, photometry is performed using the imaging signal 10c supplied from the signal processing unit 114 to the system control unit 12 as it is. Is called. Next, based on the photometric value calculated by the control unit 12 and converted into a digital signal, the exposure amount is calculated by the exposure calculation control function unit 12A of the system control unit 12, and a substantial exposure time for achieving this exposure amount is determined. Is done. In order to ensure the exposure time, the system control unit 12 can supply a control signal 12a for determining the timing for closing the mechanical shutter 108d to the AE adjustment unit 108.
[0039]
Here, when determining the closing timing of the mechanical shutter, it is considered that it takes a certain time to close the mechanical shutter. That is, the mechanical shutter cannot be closed at a desired timing without considering the delay from when the closing timing signal 12a is issued until the actual closing operation is started and the time required until the mechanical shutter is completely closed ( Hereinafter, these are collectively referred to as “mechanical shutter closing time”). Therefore, the system control unit 12 calculates a substantial exposure time for obtaining an appropriate exposure amount as “substantial exposure time = mechanical shutter opening time + mechanical shutter closing time”, and takes the mechanical shutter closing time into consideration earlier. The closing signal 12a is supplied to the AE adjusting unit 108. This adjustment can optimize the exposure. Further, as will be described later in the explanation of the operation of the present embodiment, the exposure mode length can be matched with this substantial exposure time.
[0040]
The timing at which the mechanical shutter is opened can also be controlled by the control unit 12 by sending an open signal 12a to the AE adjustment unit 108. At this time, it is possible to control the AE adjustment unit 108 so that the mechanical shutter 108d opens at the same time as reading of the signal charge accumulated in the imaging unit 104 at the latest, and the timing signal generation unit 120 switches to the exposure mode again at the same time as reading is completed. The timing signal generator 120 can be controlled to perform the above. These controls enable continuous shooting.
[0041]
The drive signal generation unit 10C includes a timing signal generation unit 120 connected to the outputs 12d and 12e of the system control unit 12, and a driver unit 122 connected to the output 120a of the generation unit 120. The timing signal generation unit 120 generates the synchronization signal 20c based on the original oscillation clock generated so that the digital still camera 10 is driven in the current broadcasting system (NTSC / PAL), for example, and sends it to the signal processing unit 114. Supply. The timing signal generator 120 also sends the timing signals 20a and 20b as clocks that serve as the operation reference for sampling signals and write / read signals to the preprocessing unit 110, the A / D conversion unit 112, the buffer unit 116, and the compression / decompression processing unit 118. , 20d, and 20e. If these timing signals can be shared, the number of components of the timing signal generation unit 120 can be reduced.
[0042]
The timing signal generation unit 120 is connected to the outputs 12d and 12e of the system control unit, generates a synchronization signal from the original oscillation clock, and further generates various timing signals 120a generated using these signals by the driver unit 122. Is output. For the output timing signal 120a, a timing signal used for reading the signal charge obtained by the imaging unit 104, for example, a vertical synchronization signal VD for supplying the driving timing of the vertical transfer path, and a driving timing of the horizontal transfer path are supplied. There are a horizontal synchronization signal HD, a timing pulse for field shift and line shift, a charge extraction pulse for an electronic shutter, and operation mode information.
[0043]
It is the timing signal generator 120 that determines the operation mode of the camera 10. The generation unit 120 is normally in the movie mode, and when receiving the mode switching instruction 12d from the control unit 12, the generation unit 120 switches the operation mode in synchronization with the next vertical synchronization signal VD transmitted by itself. However, when a reset pulse is sent from the system control unit through the signal line 12e simultaneously with the mode switching instruction 12d, for example, the vertical synchronization signal VD is reset, so that the operation mode is switched simultaneously with the mode switching instruction 12d.
[0044]
The driver unit 122 is connected to the output 120a from the timing signal generation unit 120, and generates a drive signal 122a for the imaging unit 104 based on the various signals 120a. At this time, the driver unit 122 can be set to perform an operation specific to the present invention. That is, when the operation mode is switched from the movie mode to the exposure mode, at the same time, it can be set to output a charge extraction pulse (electronic shutter pulse) of a fixed number of times one or more times over a predetermined period. is there. When the operation mode is switched to the signal readout mode, the imaging unit 104 is instructed to read out signal charges.
[0045]
The driver unit 122 also outputs the vertical synchronization signal VD and the horizontal synchronization signal HD to the system control unit 12 through the signal line 122b. This is because a CPU (not shown) in the system control unit counts these timing signals, thereby outputting the mode switching instruction 12d and the reset pulse 12e.
[0046]
The operation of the embodiment of the present invention configured as described above will be described below.
[0047]
First, the prior art will be described for comparison. The hardware configuration of this prior art is not shown, but if necessary, refer to Japanese Patent No. 2649882 and Japanese Patent No. 2649883. FIG. 2 shows a time chart of the prior art in which exposure is started with an electronic shutter and exposure is ended with a mechanical shutter. In FIG. 2, when a still image shooting command is issued, the vertical synchronizing signal VD shown in FIG. 2 (a) is synchronized with the timing 200 at which the negative polarity immediately after the command is turned, as shown in FIG. 2 (e). Then, switching from the previous operation mode to the exposure mode 202 is performed.
[0048]
Here, an error occurs in the exposure time due to delay variation in the mechanical shutter closing time. That is, even if a closing pulse is given to the mechanical shutter at the timing 204, the immediate closing operation as shown by the dotted line 206 is not performed, and the closing operation is performed with a slight delay. Accordingly, there is a possibility that a delay corresponding to the time indicated by reference numeral 208 is generated, and an excess charge is generated as the exposure time becomes longer, resulting in an overflow.
[0049]
Therefore, in the prior art, fine adjustment 210 is performed on the electronic shutter side where exposure is started using a vertical overflow drain structure so that an appropriate exposure amount can be obtained. While the electronic shutter pulse is being applied, the charge of the CCD is repeatedly extracted, and the charge becomes zero each time and the charge accumulation is restarted. Thus, the exposure start is delayed by a necessary time, and the delay variation of the mechanical shutter is compensated to obtain a substantial exposure time (mechanical shutter opening time + mechanical shutter closing time) 211. This fine adjustment 210 is performed after a substantial exposure time 211 is grasped in advance by using a conventional photometric mechanism.
[0050]
However, in such a method of compensating for the mechanical shutter delay on the electronic shutter side, the time lag 212 from the start of the exposure mode 202 to the start of actual exposure becomes longer. In particular, in the case of a bright subject, the surplus charge increases, so that the electronic shutter needs to frequently extract the charge, and the output frequency becomes dense. As a result, there is a drawback that an object moving at an ultra high speed is missed. In addition, the exposure mode 202 is unnecessarily extended due to this time lag, and there is a disadvantage that the number of images is reduced when continuous shooting is performed.
[0051]
FIG. 3 is a time chart of the first embodiment of the exposure method according to the present invention, which solves the problems of the prior art as described above. The operation of the present embodiment will be described below with reference to FIG. In this embodiment, the timing signal generator 120 of FIG. 1 is initially in the movie mode. When the metering instruction signal 28 is sent to the system control unit 12 by half-pressing the shutter release button 128, the exposure calculation control function unit 12A uses the imaging signal 10c supplied from the signal processing unit 114 to the system control unit 12. And measure the light. The system control unit 12 determines a substantial exposure time so as to achieve an exposure amount based on the calculated photometric value, and based on this, a control signal 12a for determining the timing for closing the mechanical shutter 108d is sent to the AE adjustment unit 108. Supply. The timing here is the timing 222 of the rise of the mechanical shutter drive pulse in FIG. It is set to drive earlier than the rise timing 224 of the mechanical shutter drive pulse before adjustment shown in FIG.
[0052]
When the shutter release button 128 is fully pressed, an exposure mode switching signal 28 is transmitted, and the system control unit 12 sends this to the timing signal generation unit 120 as an exposure mode switching instruction 12d. The timing signal generation unit 120 switches to the exposure mode in synchronization with the timing 226 at which the immediately following vertical synchronization signal VD changes to negative polarity, and outputs the switched mode information to the driver unit 122. The driver unit 122 gives the electronic shutter output pulse 122a a fixed number of times one or more times to the imaging unit, and starts actual exposure from the fixed time point 228. In this way, the charge extraction pulse to the electronic shutter shown in FIG. 3B may be output any number of times, but as described above, the fixed number of times is used. Therefore, the exposure start time is fixed at an early time. The end of exposure is performed by the mechanical shutter 108d adjusted by photometry as described above. By substantially closing the mechanical shutter 108d, the substantial exposure time 232 is advanced. That is, the delay of the mechanical shutter 108d is compensated not by the electronic shutter but by the mechanical shutter itself. As a result, the actual exposure time 232 is not different from the conventional one, but the time lag 230 from the start of the exposure mode to the actual start of exposure is much shorter than that of the prior art.
[0053]
FIG. 4 is a time chart of the second embodiment of the exposure method according to the present invention. In this embodiment, unlike FIG. 3, the exposure start time is determined by generating a field shift pulse instead of an electronic shutter. The same operation timing as that in FIG. 3 is represented using the same reference numerals as in FIG. 4 differs from FIG. 3 in that, simultaneously with the shift to the exposure mode 220, the driver unit 122 applies the field shift pulse 122a to the transfer gate of the imaging unit 104 instead of the electronic shutter pulse. As a result, unnecessary charges accumulated in the imaging device of the imaging unit 104 are field-shifted to the vertical transfer path.
[0054]
In this embodiment, the actual exposure is started substantially simultaneously with the transition to the exposure mode 220 as described above. Corresponding to this, the drive timing of the mechanical shutter 108d is also earlier than that of FIG. 3, the drive pulse is started at the timing 236, and the closing is started at the timing 238. Thus, the present embodiment has an advantage that the time lag is substantially eliminated. In this embodiment, the electronic shutter mechanism used in FIG. 3 is not necessary. However, the operation as in the present embodiment can also be realized using an electronic shutter pulse. In that case, the electronic shutter pulse may be output only once at the same time as the shift to the exposure mode.
[0055]
When the field shift pulse is used to specify the exposure start time as in this embodiment, the charge shifted to the vertical transfer path is swept from the vertical transfer path before the start of the signal readout mode 234. It is necessary.
[0056]
FIG. 5 is a time chart showing a third embodiment of the exposure method according to the present invention. The timing signal generator 120 in FIG. 1 is initially in the movie mode 300 in FIG. When the shutter release button 128 is half-pressed, a photometry instruction signal 28 is input to the system control unit 12. Thereby, the exposure calculation control function unit 12A performs photometry using the imaging signal 10c supplied from the signal processing unit 114 to the system control unit 12.
[0057]
The feature of the present embodiment is that AE (Auto Exposure) information acquired at the time of the movie mode 300 before moving to exposure, specifically, based on the imaging signal 10c supplied to the system control unit 12, performs photometry, The length of the exposure mode 304 is determined. In this respect, the present embodiment differs from the embodiment of FIG. 3 or FIG. 4 in that not only the substantial exposure time is calculated, but also the length of the exposure mode 304 is shortened to match this. That is, “exposure mode length = substantial exposure time = mechanical shutter opening time + mechanical shutter closing time”, and the exposure mode 304 is maintained only for the calculated exposure time. The system control unit 12 supplies a control signal 12a for determining the timing for closing the mechanical shutter 108d to the AE adjustment unit 108 so as to achieve the calculated substantial exposure time.
[0058]
When the shutter release button 128 is fully pressed, a switching signal 28 to the exposure mode is transmitted. When the system control unit 12 sends this to the timing signal generation unit 120 as a mode switching instruction 12d, this appears as a shooting command 302 in the vertical synchronization signal VD of FIG. At the same time, the system control unit 12 starts measuring the exposure mode 304. Thereby, the shift to the exposure mode 304 of FIG. Simultaneously with the transition to the exposure mode 304, the driver unit 122 outputs the electronic shutter pulse 305 once and immediately starts actual exposure. As shown in FIG. 3, the electronic shutter can be output a fixed number of times from the transition to the exposure mode, but here, the useless exposure mode length is reduced and the exposure mode length is substantially reduced. To match the exposure time, the output is only once. The end of exposure is performed by the mechanical shutter 108d adjusted by photometry. As described above, the charge extraction pulse to the electronic shutter shown in FIG. 5B is output only once, and the start of the substantial exposure time 306 coincides with the start of the exposure mode 304.
[0059]
At the same time as the exposure time calculated in advance elapses, the system control unit 12 uses the signal 12e in FIG. 1 to generate the timing signal generation unit 120 regardless of the normal frequency of the vertical synchronization signal VD in FIG. On the other hand, the reset output 308 of the forced vertical synchronizing signal VD is instructed. The exposure time by the system control unit 12 may be measured by counting the synchronization signal as shown in FIG. FIGS. 8A and 8C are enlarged views of FIGS. 5A and 5C, and FIGS. 8B and 8D are output timings of the horizontal synchronization signal HD and the reset pulse. As shown in FIG. 8, the transition to the exposure mode 304, that is, simultaneously with the timing 302 of the vertical synchronization signal VD shown in FIG. 8A, the horizontal synchronization signal HD in the period 307 shown in FIG. It may be performed by counting (provided from the driver section by one signal line 122b). When a predetermined number of signals HD are counted, a reset pulse 303 shown in FIG. 8D is output. This appears as the output 308 of the signal VD in FIG.
[0060]
As a result, the start of the exposure mode coincides with the start of the actual exposure to eliminate the time lag, and at the same time as the actual exposure ends, the exposure mode is also forcibly terminated and immediately shifts to the signal readout mode 310. can do. In FIG. 5, it can be seen that the exposure mode itself is shorter than in FIG. 3 or FIG. Therefore, the exposure time can be further shortened.
[0061]
FIG. 6 is a time chart showing a fourth embodiment of the exposure method according to the present invention. The operation of this embodiment is substantially the same as that of the third embodiment of FIG. 5, and the same pulse and timing are denoted by the same reference numerals. 6 differs from FIG. 5 in that the exposure is started not by the electronic shutter but by the transfer gate of FIG. 6 (c). Only differences from FIG. 5 will be described below.
[0062]
In FIG. 6, the process is the same as that in FIG. 5 until the movie mode 300 shifts to the exposure mode 304. Simultaneously with the start of the exposure mode 304, in this embodiment, the field shift pulse 312 is output to the transfer gate of FIG. 6C instead of the electronic shutter pulse of FIG. 6B. Thereby, exposure is started. Unnecessary signal charges swept out to a vertical transfer path (not shown) of the imaging unit 104 in FIG. 1 by the field shift pulse 312 are transferred vertically and horizontally during the substantial exposure time 306 and discarded. Similar to FIG. 5, the exposure mode 304 is adjusted to the substantial exposure time 306 started by the field shift pulse 312, and a forced reset pulse 308 is applied to the vertical synchronization signal VD of FIG. 6A. Thus, the exposure mode is shifted to the signal readout mode 310 in the shortest time.
[0063]
FIG. 7 is a time chart showing a fifth embodiment of the exposure method according to the present invention. This embodiment shows an exposure method when continuous shooting is performed using the fourth embodiment of FIG. 6 (exposure is started by a field shift pulse). However, the third embodiment shown in FIG. 5 (exposure is started by an electronic shutter) can also realize the embodiment that performs continuous shooting shown in FIG.
[0064]
Hereinafter, only the points of FIG. 7 different from those of FIG. 6 will be described. For the same pulse and timing, the same reference numerals as in FIG. 6 are used. The operation until the exposure mode 304 is made to coincide with the substantial exposure time 306, and the reset pulse 308 is output simultaneously with the end of the exposure to forcibly shift to the signal readout mode is the same as in FIG.
[0065]
Thereafter, the signal charge is read out in the signal readout mode 310, and the last vertical synchronization signal 314 in the signal readout mode 310 is output, so that the signal charge from the vertical transfer path is completely read out, for example, at any time 318. In addition, the system control unit 12 identifies the state of the shutter release button 128 again. At this time, if the shutter release button 128 has been returned to a state other than full press, the system control unit 12 returns the timing signal generation unit 120 to the movie mode.
[0066]
However, when continuous shooting is performed as in the present embodiment, the shutter release button 128 is kept fully pressed. In this case, the system control unit 12 gives the opening timing of the mechanical shutter 108d as the control signal 12a to the AE adjusting unit 108 so that the mechanical shutter 108d is opened simultaneously with the completion of reading of the signal charge. The AE adjustment unit 108 inverts the mechanical shutter drive pulse of FIG. 7D at timing 320, applies this to the mechanical shutter as a drive signal 108c, and opens the mechanical shutter simultaneously with the end of signal readout (start of exposure mode 316). On the other hand, the timing signal generation unit 120 is again set to the exposure mode 316 and repeats the same operations as those performed in the previous exposure mode 304 and signal readout mode 310. That is, the exposure mode switching instruction 12d is sent to the timing signal generation unit 120, and the generation unit 120 switches to the exposure mode 316 again. The field shift pulse 322 is output simultaneously with the start of the exposure mode 316 to start substantial exposure, and the mechanical shutter drive pulse 323 is output according to the exposure time 326 based on the AE information that the system control unit 12 already has. Then, the mechanical shutter 108d is completely closed simultaneously with the end of the exposure time 326. At the same time, a reset pulse 324 is output from the system controller 12 to the timing signal generator, and the exposure mode 316 is forcibly terminated simultaneously with the end of the substantial exposure 326. Then, the signal reading mode 328 is started. Thereby, the exposure mode and the signal readout mode are repeated in the shortest time, and the advantage that the number of continuous shots increases can be obtained.
[0067]
The embodiment of the present invention has been described above using a digital camera. However, the present invention is not limited to the above-described embodiments, and can be applied to all types of imaging devices in which the exposure start time is performed by an electronic shutter or a transfer gate and the exposure end time is performed by a mechanical shutter.
[0068]
【The invention's effect】
Thus, according to the present invention, substantial exposure can be started with a small time lag from the shift to the exposure mode. This improves the feeling of use. In addition, since the electronic shutter is output only a fixed number of times, the number of cases where a fast-moving subject is missed is also reduced. On the other hand, when the field shift pulse is output to the transfer gate instead of the electronic shutter and the exposure start timing is obtained, the same effect can be obtained. In this case, the electronic shutter and related circuits are not required.
[0069]
Furthermore, the exposure mode length can be made equal to the substantial exposure time. That is, the substantial exposure can be started simultaneously with the shift to the exposure mode, and the exposure mode can be forcibly terminated simultaneously with the end of the substantial exposure. Thereby, the time lag is substantially removed, and the photographing time is shortened. Therefore, there is an advantage that the number of continuous shots increases especially when continuous shooting is performed.
[0070]
In addition, the charge accumulated in the image sensor by exposure can be transferred to the vertical transfer path in the shortest time, so that charge loss can be prevented and saturation of the image sensor can be prevented.
[0071]
In addition, the mechanical shutter used by the imaging apparatus according to the present invention can be mounted anywhere on the camera, and is less subject to mounting location restrictions than the electronic shutter.
[0072]
Furthermore, when exposure is performed only with an electronic shutter pulse, so-called white flaws appear on the screen, and the present invention in which exposure is terminated using a mechanical shutter has the advantage of not affecting the image quality.
[Brief description of the drawings]
FIG. 1 is a block diagram in which an imaging apparatus according to the present invention is applied to a digital camera.
FIG. 2 is a time chart of the prior art.
FIG. 3 is a time chart of the first embodiment of the exposure method according to the present invention.
FIG. 4 is a time chart of the second embodiment of the exposure method according to the present invention.
FIG. 5 is a time chart of a third embodiment of the exposure method according to the present invention.
FIG. 6 is a time chart of a fourth embodiment of the exposure method according to the present invention.
FIG. 7 is a time chart of the fifth embodiment of the exposure method according to the present invention.
8 is a diagram illustrating an output timing of a reset pulse output by the system control unit of FIG.
[Explanation of symbols]
10 Digital camera
12 System controller
104 Imaging unit
108 AE adjustment section
120 Timing signal generator
122 Driver section
128 Shutter release button

Claims (7)

Includes a plurality of two-dimensional image sensors that photoelectrically convert incident light from the object field into signal charges and store them, and operates according to at least an operation mode selected from the movie mode, exposure mode, or signal readout mode In the imaging apparatus, the apparatus further includes:
Exposure calculation means for calculating an exposure time of the image sensor based on the amount of incident light irradiated from the object field;
Charge extraction means for extracting signal charges accumulated in the imaging device;
When the operation mode is switched from the movie mode to the exposure mode, at the same time, a charge extraction instruction is given to the charge extraction unit at least once over a predetermined period, and when the operation mode is switched to the signal readout mode, Signal generating means for instructing the image sensor to read out the accumulated signal charge;
Mechanical shutter means for physically blocking the imaging device from the object scene by a mechanical shutter drive pulse indicating closing ;
Exposure adjusting means for adjusting exposure by opening and closing the mechanical shutter means;
When the operation mode is switched and the operation mode is normally set to the movie mode and the operation mode is switched to the exposure mode, the time from the end of the charge extraction over the predetermined period until the mechanical shutter means is closed is calculated. to be equal to the exposure time, and a control means for changing the time of closing the mechanical shutter means determines the closing timing of the mechanical shutter driving pulse based on the exposure time, and controls the exposure adjustment means ,
An image pickup apparatus, wherein exposure is performed by switching to an exposure mode by the control unit, and signal charge is read by switching to a signal readout mode by the control unit.   2. The image pickup apparatus according to claim 1, wherein the exposure over the exposure time is performed by controlling the time of closing the mechanical shutter means by the control means.   3. The image pickup apparatus according to claim 1, wherein exposure is started simultaneously with switching to the exposure mode when the charge extracting unit extracts the signal charge only once. 4. The image pickup apparatus according to claim 1, wherein the charge extracting unit is an electronic shutter that discards signal charges in a direction of a substrate on which the image pickup element is arranged. 4. The image pickup apparatus according to claim 1, wherein the charge extracting unit is a transfer gate that moves a signal charge to a charge transfer path provided in parallel with the image pickup element. . A movie process for irradiating a plurality of image pickup elements arranged in two dimensions with incident light from an object scene, and exposure is started by extracting charges accumulated in the image pickup element, and mechanical shutter means is closed and the image pickup is performed. In the exposure method including an exposure step of terminating exposure by physically blocking the element from the object field, and a signal reading step of reading out signal charges accumulated in the imaging device by the exposure, the exposure step includes:
At the same time as switching from the movie process to the exposure process, an electronic shutter process that starts exposure by extracting signal charges from the image sensor at least once over a predetermined period;
Closing the mechanical shutter means simultaneously with the elapse of a desired exposure time by a mechanical shutter drive pulse indicating closing ,
An exposure method comprising: determining a closing timing of the mechanical shutter drive pulse based on the exposure time, changing a time point of closing the mechanical shutter means, and controlling the closing step.   7. The method according to claim 6, wherein, in the electronic shutter process, simultaneously with switching to the exposure process, the signal charge is extracted from the imaging device only once at the same time as switching to the exposure process. An exposure method characterized by starting exposure.

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